Periodic Stimuli Research Articles

Frequency-dependent dynamics of steady-state visual evoked potentials under sustained flicker stimulation

Steady-state visual evoked potentials (SSVEP) are electroencephalographic signals elicited when the brain is exposed to a visual stimulus with a steady frequency. We analyzed the temporal dynamics of SSVEP during sustained flicker stimulation at 5, 10, 15, 20 and 40 Hz. We found that the amplitudes of the responses were not stable over time. For a 5 Hz stimulus, the responses progressively increased, while, for higher flicker frequencies, the amplitude increased during the first few seconds and often showed a continuous decline afterward. We hypothesize that these two distinct sets of frequency-dependent SSVEP signal properties reflect the contribution of parvocellular and magnocellular visual pathways generating sustained and transient responses, respectively. These results may have important applications for SSVEP signals used in research and brain-computer interface technology and may contribute to a better understanding of the frequency-dependent temporal mechanisms involved in the processing of prolonged periodic visual stimuli.

Field-Programmable Analog Array Implementation of Neuromorphic Silicon Neurons with Fractional Dynamics

Silicon neurons are bioinspired circuits with the capability to reproduce the modulation through pulse-frequency observed in real neurons. They are of particular interest in closed-loop schemes to encode the control signal into pulses. This paper proposes the analog realization of neuromorphic silicon neurons with fractional dynamics. In particular, the fractional-order (FO) operator is introduced into classical neurons with the intention of reproducing the adaptation that has been observed experimentally in real neurons, which is the variation in the firing frequency even when considering a constant or periodic incoming stimulus. For validation purposes, simulations using a field-programmable analog array (FPAA) are performed to verify the behavior of the circuits.

The role of stimulus periodicity on spinal cord stimulation-induced artificial sensations in rodents

Objective. Sensory feedback is critical for effectively controlling brain-machine interfaces and neuroprosthetic devices. Spinal cord stimulation (SCS) is proposed as a technique to induce artificial sensory perceptions in rodents, monkeys, and humans. However, to realize the full potential of SCS as a sensory neuroprosthetic technology, a better understanding of the effect of SCS pulse train parameter changes on sensory detection and discrimination thresholds is necessary. Approach. Here we investigated whether stimulation periodicity impacts rats’ ability to detect and discriminate SCS-induced perceptions at different frequencies. Main results. By varying the coefficient of variation (CV) of interstimulus pulse interval, we showed that at lower frequencies, rats could detect highly aperiodic SCS pulse trains at lower amplitudes (i.e. decreased detection thresholds). Furthermore, rats learned to discriminate stimuli with subtle differences in periodicity, and the just-noticeable differences from a highly aperiodic stimulus were smaller than those from a periodic stimulus. Significance. These results demonstrate that the temporal structure of an SCS pulse train is an integral parameter for modulating sensory feedback in neuroprosthetic applications.

A numerical study of a single isolated human ventricular cell response to a periodic pulse stimulus current using the Rogers–McCulloch model

Among the primary causes of cardiac arrhythmias are abnormalities in the generation of action potentials (APs) by the cardiac cells, which may be induced by alterations in the electrophysiological properties of the cells as well as the stimuli delivered to them. Through numerical simulations using the phenomenological model of Rogers–McCulloch, this study examined how external stimuli modulate the electrical activity of a single isolated human ventricular cell functioning under normal conditions. First, we investigated how the initial conditions of the two model state variables affect how the cell responds to a single rectangular current pulse. This allows for the determination of a critical curve, which separates the initial conditions that allow for AP activation from those that inhibit it. This critical curve can be used to predict AP activation not only when the cell is stimulated by a single current pulse but also by a periodic stimulus. Then, we examined the cell response to a periodic train of rectangular current pulses, with a focus on the effects of the stimulus pacing length and amplitude. Our findings demonstrated that, despite not considering any alteration in the dynamics of ionic currents through the cell membrane, the Rogers–McCulloch model was capable of reproducing some of the most common activation patterns that have been widely identified in several clinical, experimental, and numerical studies. Depending on the stimulus properties, the following activation patterns were identified: (1) AP activation in synchrony with the stimulus, with one AP activation per pulse; (2) quasi-periodic and periodic Wenckebach-like patterns, in which successive AP activations are interrupted by a skipped beat; (3) completely irregular patterns; (4) abnormal potential oscillations that interrupt the repolarization of a previously activated AP, followed or not by a skipped beat; and (5) abnormal potential oscillations that completely inhibit cell repolarization.

Can nutritional programming in Atlantic salmon (Salmo salar) be optimised with a reduced stimulus period?

New strategies are required to enhance the efficient assimilation and bioconversion of plant-based ingredients in Atlantic salmon (Salmo salar) diets, especially relating to the essential long-chain polyunsaturated fatty acids (LC-PUFA), eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). Our study investigated nutritional programming and specifically evaluated the optimal duration of dietary ‘stimulus’ and whether it could be reduced compared to a previous study using a three- week ‘stimulus’. Fish were fed an experimental ‘stimulus’ vegetable-based diet (VS, 5% marine meals [MM]/0% fish oil [FO]) or a standard marine-based control (MS, 82% MM/4% FO) for either one (V1) or two weeks (V2 and M) from first exogenous feeding. All groups were then fed a standard marine based formulation, for an ‘intermediate’ grow-out phase to the end of 16 weeks post-first feeding, prior to a ‘challenge’ phase of six weeks when all fish were fed a vegetable-based diet (VC, 10% MM/0% FO). Compared to M, fish from both V1 and V2 groups were significantly smaller at the end of the ‘stimulus’ phase, but there were no statistical differences in overall growth, proximate or fatty acid compositions at the end of the trial. However, hepatosomatic and viscerosomatic indices were significantly lower in V1 compared to V2 fish and there was an overall trend of improved performance in V1 fish throughout the ‘intermediate’ and ‘challenge’ phases. During the ‘challenge’ phase, M fish displayed a greater net gain of DHA than V1 fish, whilst V2 was a net consumer of all n-3 LC-PUFA over the same period. Compared to M, n-3 LC-PUFA biosynthesis genes in pyloric caeca were downregulated in both experimental groups indicating possible post-transcriptional modification of this pathway in either V1 or V2, considering the differences in DHA retention levels between groups. Taken together, the results suggested that nutritional programming was not initiated by a one- or two- week ‘stimulus’. However, more studies are required to elucidate the mechanism behind enhanced performance of V1 fish.

Modeling Robotic Thinking and Creativity: A Classic–Quantum Dialogue

The human mind can be thought of as a black box, where the external inputs are elaborated in an unknown way and lead to external outputs. D’Ariano and Faggin schematized thinking and consciousness through quantum state dynamics. The complexity of mental states can be formalized through the entanglement of the so-called qualia states. Thus, the interaction between the mind and the external world can be formalized as an interplay between classical and quantum-state dynamics. Since quantum computing is more and more often being applied to robots, and robots constitute a benchmark to test schematic models of behavior, we propose a case study with a robotic dance, where the thinking and moving mechanisms are modeled according to quantum–classic decision making. In our research, to model the elaboration of multi-sensory stimuli and the following decision making in terms of movement response, we adopt the D’Ariano–Faggin formalism and propose a case study with improvised dance based on a collection of poses, whose combination is presented in response to external and periodic multi-sensory stimuli. We model the dancer’s inner state and reaction to classic stimuli through a quantum circuit. We present our preliminary results, discussing further lines of development.

Performance of Pulsating Heat Pipe with a stimulus of auxiliary heat load for Battery Thermal Management System

Stimulus strategy is proposed to enhance the heat dissipation performance of Pulsating Heat Pipe (PHP) at low heat load for local hot spot regression in Battery Thermal Management (BTM). An auxiliary heat load is applied to stimulate the start-up of PHP. The performances of PHP with and without stimulus are compared and the properties of PHP after stimulus are discussed. It is concluded that the application of auxiliary heat load is able to stimulate the start-up of PHP in experiments. The strategy is mainly based on the phase-change mechanism as well as the hysteresis of working medium. Thermal resistance and the evaporator temperature are significantly reduced, if PHP starts operation after stimulus. Long period of stimulus and strong auxiliary heat load are favored for the reduction of thermal resistance and the shortening of period for start-up. The thermal resistance may be reduced by 29.1 ∼ 69.6 % and the temperature may be regressed by around 8 °C. However, PHP may suffer from temperature uplift and overshot to the maximum evaporator temperature. Therefore, high interference temperature coupled with weak auxiliary heat load and long period of stimulus are suggested as the optimal strategy. The verified strategy offers a new method for local hot spot regression and a possible way to mitigate the risk of thermal runaway, since the heat dissipation is enhanced at the initial stage of damage or destruction.

Skin viscoelasticity effects on the periodic mechanical stimuli propagation between skin layers

Our daily lives are constantly surrounded by dynamic stimuli, and our skin is deformed in a time-dependent manner. Although skin plays an important role in transmitting stimuli received at the surface to mechanoreceptors, few studies have investigated how differences in skin viscoelasticity affect the mechanical stimuli propagation in the skin. Therefore, using a finite element model, we evaluated the effects and trends of changes in the stiffness and viscoelasticity of the skin on the propagation of mechanical quantities between skin layers where mechanoreceptors are present when subjected to periodic stimuli. First, we constructed a new, sophisticated mathematical model of skin viscoelasticity based on the history-dependent deformation behavior of human skin obtained experimentally. We were able to construct a skin model that thoroughly reproduced the actual human skin deformation behavior at oscillations as fast as 10 Hz by setting viscoelastic parameters with a short time constant (0.001–0.006 s). Then, we calculated how skin material parameters affect the propagation of the mechanical quantities in the skin during the history-dependent skin deformation response to periodic stimuli. The finite element analysis showed that not only stiffness but also viscoelasticity markedly affected the mechanical stimuli propagation in the skin, and the effect differed depending on the layer. In particular, greater immediate responsiveness of the dermis contributed to greater propagation of the mechanical stimulus. Our results indicate that more attention needs to be given to the differences in the time-dependent intradermal mechanical stimuli propagation caused by individual's skin viscoelasticity.

Thermo-capillarity of immiscible binary fluids within serpentine micro-confinements

The thermocapillary flow of multiple liquid layers over contoured substrates finds applications in many industrial phenomena via micro-electromechanical systems/nano-electromechanical systems devices. This study theoretically explores the thermocapillary transport of binary-liquid layers in a wavy microchannel with serpentine wall profiles. Sinusoidal profiles are considered for the microchannel walls' temperature and surface topology. Patterned slip conditions at the walls are also accounted for in the analysis to make the problem more realistic. We semi-analytically solve the energy and momentum equations to understand the system's thermal and hydrodynamic characteristics for the limiting conditions of Ma, Re, and Ca. The leading- and higher-order solutions of the temperature and flow field are separately shown to demonstrate the advection terms' contribution to the transport equations. The circulatory flow obtained due to periodic thermal stimuli can be used to enhance the mixing efficiency of the system. We also present how the parameters like phase difference between the thermal stimulus, relative thermal conductivity, and relative film thickness ratio of the liquid layers can be altered to control the flow characteristics to obtain the most potent thermocapillary effect.

Improving the performance of P300-based BCIs by mitigating the effects of stimuli-related evoked potentials through regularized spatial filtering

Objective. the P300-based brain–computer interface (BCI) establishes a communication channel between the mind and a computer by translating brain signals into commands. These systems typically employ a visual oddball paradigm, where different objects (linked to specific commands) are randomly and frequently intensified. Upon observing the target object, users experience an elicitation of a P300 event-related potential in their electroencephalography (EEG). However, detecting the P300 signal can be challenging due to its very low signal-to-noise ratio (SNR), often compromised by the sequence of visual evoked potentials (VEPs) generated in the occipital regions of the brain in response to periodic visual stimuli. While various approaches have been explored to enhance the SNR of P300 signals, the impact of VEPs has been largely overlooked. The main objective of this study is to investigate how VEPs impact P300-based BCIs. Subsequently, the study aims to propose a method for EEG spatial filtering to alleviate the effect of VEPs and enhance the overall performance of these BCIs. Approach. our approach entails analyzing recorded EEG signals from visual P300-based BCIs through temporal, spectral, and spatial analysis techniques to identify the impact of VEPs. Subsequently, we introduce a regularized version of the xDAWN algorithm, a well-established spatial filter known for enhancing single-trial P300s. This aims to simultaneously enhance P300 signals and suppress VEPs, contributing to an improved overall signal quality. Main results. analyzing EEG signals shows that VEPs can significantly contaminate P300 signals, resulting in a decrease in the overall performance of P300-based BCIs. However, our proposed method for simultaneous enhancement of P300 and suppression of VEPs demonstrates improved performance in P300-based BCIs. This improvement is verified through several experiments conducted with real P300 data. Significance. this study focuses on the effects of VEPs on the performance of P300-based BCIs, a problem that has not been adequately addressed in previous studies. It opens up a new path for investigating these BCIs. Moreover, the proposed spatial filtering technique has the potential to further enhance the performance of these systems.

Effects of Stimulus Rate and Periodicity on Auditory Cortical Entrainment to Continuous Sounds.

The neural mechanisms underlying the exogenous coding and neural entrainment to repetitive auditory stimuli have seen a recent surge of interest. However, few studies have characterized how parametric changes in stimulus presentation alter entrained responses. We examined the degree to which the brain entrains to repeated speech (i.e., /ba/) and nonspeech (i.e., click) sounds using phase-locking value (PLV) analysis applied to multichannel human electroencephalogram (EEG) data. Passive cortico-acoustic tracking was investigated in N = 24 normal young adults utilizing EEG source analyses that isolated neural activity stemming from both auditory temporal cortices. We parametrically manipulated the rate and periodicity of repetitive, continuous speech and click stimuli to investigate how speed and jitter in ongoing sound streams affect oscillatory entrainment. Neuronal synchronization to speech was enhanced at 4.5 Hz (the putative universal rate of speech) and showed a differential pattern to that of clicks, particularly at higher rates. PLV to speech decreased with increasing jitter but remained superior to clicks. Surprisingly, PLV entrainment to clicks was invariant to periodicity manipulations. Our findings provide evidence that the brain's neural entrainment to complex sounds is enhanced and more sensitized when processing speech-like stimuli, even at the syllable level, relative to nonspeech sounds. The fact that this specialization is apparent even under passive listening suggests a priority of the auditory system for synchronizing to behaviorally relevant signals.

The Effects of Auditory, Visual, and Cognitive Distractions on Cybersickness in Virtual Reality.

Cybersickness (CS) is one of the challenges that has hindered the widespread adoption of Virtual Reality (VR). Consequently, researchers continue to explore novel means to mitigate the undesirable effects associated with this affliction, one that may require a combination of remedies as opposed to a solitary stratagem. Inspired by research probing into the use of distractions as a means to control pain, we investigated the efficacy of this countermeasure against CS, studying how the introduction of temporally time-gated distractions affects this malady during a virtual experience featuring active exploration. Downstream of this, we discuss how other aspects of the VR experience are affected by this intervention. We discuss the results of a between-subjects study manipulating the presence, sensory modality, and nature of periodic and short-lived (5-12 seconds) distractor stimuli across 4 experimental conditions: (1) no-distractors (ND); (2) auditory distractors (AD); (3) visual distractors (VD); (4) cognitive distractors (CD). Two of these conditions (VD and AD) formed a yoked control design wherein every matched pair of 'seers' and 'hearers' was periodically exposed to distractors that were identical in terms of content, temporality, duration, and sequence. In the CD condition, each participant had to periodically perform a 2-back working memory task, the duration and temporality of which was matched to distractors presented in each matched pair of the yoked conditions. These three conditions were compared to a baseline control group featuring no distractions. Results indicated that the reported sickness levels were lower in all three distraction groups in comparison to the control group. The intervention was also able to both increase the amount of time users were able to endure the VR simulation, as well as avoid causing detriments to spatial memory and virtual travel efficiency. Overall, it appears that it may be possible to make users less consciously aware and bothered by the symptoms of CS, thereby reducing its perceived severity.

P135: Electroencephalography-Based Neuro-emotional Responses during interactive scenario therapy in the person with dementia – case study

Background:Immersive technologies have the potential to control cognitive and behavioural symptoms in people with dementia. A safe environment can be designed through a specific interactive scenario, according to the preferences and experiences of each user.Objective:Mapping neuro-emotional responses during the interactive scenario therapy experience in a case study, with dementia, using electroencephalography (EEG).Methods:A participant, 78 years old and diagnosed with moderate to severe Alzheimer's disease (female; Mini Mental State Examination score of 17 points; frontal assessment battery score of 8 points), underwent EEG analysis (EMOTIV EPOC X) using a protocol with interactive scenarios tailored to the participant's needs and preferences, the scenarios were designed from reminiscence strategies. The protocol included a stimulus that alternated between motor and cognitive activities (3 minutes), and breath-centered relaxation (1 minute). The scenarios used in this study were: setting up a living room; composing a cake recipe; shopping in the market to make a cake; looking for objects in the park; organizing a birthday party. These variables are provided, on a scale of 0 to 100, after processing by the algorithms of the EmotivPRO v3.0 software.Results:The values found in the EEG analysis will be described without stimulus and with stimulus respectively. Thus, engagement (68.57 to 71.86); arousal (57.86 to 49.86), focus (61.57 to 57.00), interest (54.86 to 49.57), relaxation (33.86 to 30.86), and stress (53.71 to 43.00). The EEG data showed an increase in engagement when the patient was stimulated (68.57 to 71.86). Relaxation also increased (30.86 to 33.86) when the stimulus was removed. The stress level, as analysed by the EEG, was also higher in the period without stimulus and reduced in the period with the stimulus (53.71 to 43).Conclusion:During a stimulus period in interactive therapy, there was an increase in engagement, which was related to an increasing focus during the stimulus. Lower values were observed compared to the period without stimulus, indicating a period of recovery after a period of concentration/arousal. Therefore, therapy with an interactive and familiar scenario, using a circuit of stimulus-breathing exercises, promotes a positive and adequate neuro-emotional response in a person with dementia.

Dynamics and maintenance of categorical responses in primary auditory cortex during task engagement.

Grouping sets of sounds into relevant categories is an important cognitive ability that enables the association of stimuli with appropriate goal-directed behavioral responses. In perceptual tasks, the primary auditory cortex (A1) assumes a prominent role by concurrently encoding both sound sensory features and task-related variables. Here, we sought to explore the role of A1 in the initiation of sound categorization, shedding light on its involvement in this cognitive process. We trained ferrets to discriminate click trains of different rates in a Go/No-Go delayed categorization task and recorded neural activity during both active behavior and passive exposure to the same sounds. Purely categorical response components were extracted and analyzed separately from sensory responses to reveal their contributions to the overall population response throughout the trials. We found that categorical activity emerged during sound presentation in the population average and was present in both active behavioral and passive states. However, upon task engagement, categorical responses to the No-Go category became suppressed in the population code, leading to an asymmetrical representation of the Go stimuli relative to the No-Go sounds and pre-stimulus baseline. The population code underwent an abrupt change at stimulus offset, with sustained responses after the Go sounds during the delay period. Notably, the categorical responses observed during the stimulus period exhibited a significant correlation with those extracted from the delay epoch, suggesting an early involvement of A1 in stimulus categorization.

Sensitivity to direction and velocity of fast frequency chirps in the inferior colliculus of awake rabbit

Neurons in the mammalian inferior colliculus (IC) are sensitive to the velocity (speed and direction) of fast frequency chirps contained in Schroeder-phase harmonic complexes (SCHR). However, IC neurons are also sensitive to stimulus periodicity, a prominent feature of SCHR stimuli. Here, to disentangle velocity sensitivity from periodicity tuning, we introduced a novel stimulus consisting of aperiodic random chirps. Extracellular, single-unit recordings were made in the IC of Dutch-belted rabbits in response to both SCHR and aperiodic chirps. Rate-velocity functions were constructed from aperiodic-chirp responses and compared to SCHR rate profiles, revealing interactions between stimulus periodicity and neural velocity sensitivity. A generalized linear model analysis demonstrated that periodicity tuning influences SCHR response rates more strongly than velocity sensitivity. Principal component analysis of rate-velocity functions revealed that neurons were more often sensitive to the direction of lower-velocity chirps and were less often sensitive to the direction of higher-velocity chirps. Overall, these results demonstrate that sensitivity to chirp velocity is common in the IC. Harmonic sounds with complex phase spectra, such as speech and music, contain chirps, and velocity sensitivity would shape IC responses to these sounds.

Exploring the dynamics of intentional sensorimotor desynchronization using phasing performance in music.

Humans tend to synchronize spontaneously to rhythmic stimuli or with other humans, but they can also desynchronize intentionally in certain situations. In this study, we investigate the dynamics of intentional sensorimotor desynchronization using phasing performance in music as an experimental paradigm. Phasing is a compositional technique in modern music that requires musicians to desynchronize from each other in a controlled manner. A previous case study found systematic nonlinear trajectories in the phasing performance between two expert musicians, which were explained by coordination dynamics arising from the interaction between the intrinsic tendency of synchronization and the intention of desynchronization. A recent exploratory study further examined the dynamics of phasing performance using a simplified task of phasing against a metronome. Here we present a further analysis and modeling of the data from the exploratory study, focusing on the various types of phasing behavior found in non-expert participants. Participants were instructed to perform one phasing lap, and individual trials were classified as successful (1 lap), unsuccessful (> 1 laps), or incomplete (0 lap) based on the number of laps made. It was found that successful phasing required a gradual increment of relative phase and that different types of failure (unsuccessful vs. incomplete) were prevalent at slow vs. fast metronome tempi. The results are explained from a dynamical systems perspective, and a dynamical model of phasing performance is proposed which captures the interaction of intrinsic dynamics and intentional control in an adaptive-frequency oscillator coupled to a periodic external stimulus. It is shown that the model can replicate the multiple types of phasing behavior as well as the effect of tempo observed in the human experiment. This study provides further evidence that phasing performance is governed by the nonlinear dynamics of rhythmic coordination. It also demonstrates that the musical technique of phasing provides a unique experimental paradigm for investigating human rhythmic behavior.

Detecting a periodic signal by a population of spiking neurons in the weakly nonlinear response regime

Motivated by experimental observations, we investigate a variant of the cocktail party problem: the detection of a weak periodic stimulus in the presence of fluctuations and another periodic stimulus which is stronger than the periodic signal to be detected. Specifically, we study the response of a population of stochastic leaky integrate-and-fire (LIF) neurons to two periodic signals and focus in particular on the question, whether the presence of one of the stimuli can be detected from the population activity. As a detection criterion, we use a simple threshold-crossing of the population activity over a certain time window. We show by means of the receiver operating characteristics (ROC) that the detectability depends only weakly on the time window of observation but rather strongly on the stimulus amplitude. Counterintuitively, the detection of the weak periodic signal can be facilitated by the presence of a strong periodic input current depending on the frequencies of the two signals and on the dynamical regime in which the neurons operate. Beside numerical simulations of the model, we present an analytical approximation for the ROC curve that is based on the weakly nonlinear response theory for a stochastic LIF neuron.Graphic abstract

Predictability awareness rather than mere predictability enhances the perceptual benefits for targets in auditory rhythms over targets following temporal cues.

Sounds following a cue or embedded in a periodic rhythm are processed more effectively than sounds that are part of an aperiodic rhythm. One might also expect that a sound embedded in a periodic rhythm is processed more effectively than a sound following a single temporal cue. Such a finding would follow the theory that the entrainment of neural rhythmic activity by periodic stimuli renders the prediction of upcoming stimuli more efficient. We conducted a psychophysical experiment in which we tested the behavioral elements of this idea. Targets in periodic and aperiodic rhythms, if they occurred, always appeared at the same moment in time, and thus were fully predictable. In a first condition, participants remained unaware of this. In a second condition, an explicit instruction on the temporal location of the targets embedded in rhythms was provided. We assessed sensitivity and reaction times to the target stimuli in a difficult temporal detection task, and contrasted performance in this task to that obtained for targets temporally cued by a single preceding cue. Irrespective of explicit information about target predictability, target detection performance was always better in the periodic and temporal cue conditions, compared to the aperiodic condition. However, we found that the mere predictability of an acoustic target within a periodic rhythm did not allow participants to detect the target any better than in a condition where the target's timing was predicted by a single temporal cue. Only when participants were made aware of the specific moment in the periodic rhythm where the target could occur, did sensitivity increase. This finding suggests that a periodic rhythm is not automatically sufficient to provide perceptual benefits compared to a condition predictable yet not rhythmic condition (a cue). In some conditions, as shown here, these benefits may only occur in interaction with other factors such as explicit instruction and directed attention.

Thermocapillary oscillations in liquid thin films: Interplay of substrate topography and thermal wave

Liquid flows over patterned and/or contoured substrates is utilized in many practical applications e.g., lubrication flow in MEMS (micro-electromechanical systems) /NEMS (nano-electromechanical systems) devices, cell sorting operations in biology, etc. The topological gradients in such geometries induce thermal gradients, which in turn generates Marangoni hydrodynamics. Here, we theoretically showcase the interplay of substrate topology, imposed wavy temperature stimulus, and chemically patterned wall slip to generate thermo-capillarity in thin liquid films. We obtain analytical solutions for the thermal and the hydrodynamic fields for low Marangoni Ma and Reynolds Re number thermocapillary effect. Vorticity is observed to generate and transport at the liquid-gas interface, and further transported to the bulk film by vertical diffusion and convection. We also study further to understand the significance of different geometric and physical parameters on the Marangoni thermo-fluid-dynamics. Interplay of constructive and destructive interference between the wave forms of the substrate topology and imposed periodic thermal stimulus may yield maximum interfacial temperature gradients and strong thermo-capillarity. It is also observed that the lower values of system Biot number Bi enables better diffusion of heat from the patterned substrate to obtain stable thermo-capillarity. Further, the presence of optimal slip patterning allows for stronger and tuned circulations in the liquid film.

The Role of Entrainment and Aperiodicity in Vibrotactile Discrimination

            The extent to which entrainment – the phenomenon in neuroscience where neurons synchronize their firing patterns to external stimuli with rhythmic or periodic features – occurs in response to aperiodic or irregular flutter stimuli remains debatable. It has been proposed by Mountcastle et al. that information is processed in a periodic manner; however, more recently, Romo et al. challenged Mountcastle’s theory and proposed that flutter stimulus was encoded based on the rapidly adapting fibers, not the periodicity.1-5 Therefore, if Mountcastle et al. is correct, the brain should be more adept at discriminating frequency between periodic stimuli than between aperiodic stimuli; conversely, if Romo et al. is correct, the brain should be equally good at discriminating frequencies between periodic and aperiodic stimuli. In this study, a two-point vibrotactile stimulation device (The Brain Gauge, Cortical Metrics, USA) was used to stimulate digits II and III of 43 participants’ preferred hand to determine their difference limen (DL) for both amplitude (AD) and frequency (FD) discrimination tests, given aperiodic or periodic stimuli. The tests were performed in the following order: periodic AD, aperiodic AD, periodic FD, and aperiodic FD. The results suggest that the periodicity of the stimuli affects frequency discrimination more than amplitude discrimination and the participants were significantly better at discriminating stimuli with periodic frequencies than aperiodic frequencies. A paired, one-tailed t-test indicated that the subject DLs resulting from periodic stimuli were significantly different (p<0.05) from that resulting from aperiodic stimuli for frequency discrimination, while it was not statistically significant for amplitude discrimination. The results were in favor of Mountcastle’s theory; however, more trials with a more controlled experimental environment may be needed to definitively conclude.